The invention generally relates to hermetic scroll compressors and more particularly to intermediate pressure designs to maintain axial compliance in scroll compressors.
U.S. Pat. No. 5,306,126 (Richardson), issued to the assignee of the present invention, is incorporated herein by reference and provides a detailed description of the operation of a typical scroll compressor.
Typically, hermetic compressors of the scroll type including a scroll mechanism which receives refrigerant at a suction pressure, compresses the received refrigerant, and discharges the compressed refrigerant at an elevated discharge pressure. Such scroll compressors are typically used in refrigeration, air conditioning and other such systems. The typical scroll mechanism includes an orbiting scroll member and a fixed scroll member, but may in an alternative form comprise co-rotating scroll members. Wraps are provided on each of the scroll members and face and intermesh with each other in an orbiting fashion so as to form pockets of compression during compressor operation.
Scroll compressors take various forms, such as high-side type compressors, wherein the internal volume of the compressor housing is primarily at discharge pressure, and low-side type compressors, wherein the internal volume is primarily at suction pressure. Efficiency in scroll mechanisms is primarily dependent upon maintaining pockets of compressed refrigerant gas during the compression cycle through to discharge with minimal leakage while consuming the least amount of energy to do so. Accordingly, it is extremely important to maintain the scroll set in a tight sealed relationship during compressor operation by maintaining the scroll set both radially and axially compliant. In some cases, when the head pressure becomes extremely high the centrifugal forces that act to keep the scroll set radially compliant are overwhelmed and radial separation occurs and when the head pressure is very low axial separation may occur.
During compressor operation, pockets of compressed gas within the scroll set act upon the wraps so as to urge them axially apart. Separation of the scroll members results in leakage and inefficient compressor operation. Preventing scroll member separation is not simply a matter of applying a pressure on the back surface of the orbiting scroll which is sufficient to maintain contact of the tips of the scroll wraps with the inside face surfaces of the scroll members. Excessive wear on the tips of the scroll wraps occurs when excessive force is applied to the back of the orbiting scroll. The compressor must operate over a wide range of operating extremes which are somewhat dependent on the refrigerant system load connected to the compressor. At the high end of the compressor's operating range, pressures are at their highest and excessive axial biasing pressure may result in excessive wear on the scroll set. At the low end of the operating range the axial forces become less and less until they are insufficient to keep the scroll set tightly engaged and leakage occurs due to the failure to maintain axial compliance.
The pressure exerted against the back of the orbiting scroll member must be great enough to maintain tip to surface contact, while being not so great so as to cause excessive wear and power consumption and further operating inefficiencies. Some compressors have been arranged so that fluid at discharge pressure is applied at a portion of the orbiting scroll member and fluid at suction pressure is applied at a second portion of the orbiting scroll member. Other attempts have been made to apply fluid at a varying, intermediate pressure, alone or in conjunction with fluid at discharge and/or suction pressures, against the back of the orbiting scroll so as to expand the operating range of the compressor. The axial compliance provided by those attempts, however, may compromised by leakage between the intermediate pressure chamber and the suction pressure chamber and/or the discharge pressure chamber. A means of improving the seal therebetween, mitigating leakage from the intermediate pressure chamber to the suction pressure chamber, and/or from the discharge pressure chamber to the intermediate pressure chamber, is desirable.